
I gathered ~30GB of AMVs from Sakuracon '03, and over the course of a couple months my friend and I went over and separated the good from the bad.
In this time, we came up with what we call the Three Rules of Three for making an AMV. The basic idea is that a video must pull from at least one of the three rules, in each rule. I'll explain in more detail after I explain the three rules.
First Rule: Sync.
Sync is *essential* to a video. Without sync you have nothing. There are, of course, three kinds of sync.
Beatsync. Beatsync is not necessarily synchronizing scene changes to beats. There are other things covered by this, including synchronizing scene changes to music, or synchronizing what is going on in a scene to the music. This does not cover lipsync. We'll get to that later.
Wordsync. Wordsync, or lyric sync, depending on how you look at it, is the art of making what is happening in your video relate to what the words in the song are saying. This can be totally flipped, ie someone singing about happiness and peace while people are getting their heads blown off for comedic effect.
Lipsync. Well, this one's pretty self explanatory, synchronizing lips to words sung. However, realize that there is a middle ground that you DO NOT WANT with this rule. Basically, if you use just a couple of scenes with lipsync, that's okay. If you use a LOT of it, that's good too. (To a point.) But if you only lipsync HALF the time, and the other half the mouths moving don't have any relation to what's going on, that's bad.
Okay! Moving on to Rule Two.
Rule Two: Concept.
Concept is also essential to an AMV. Note that this is Rule Two, which means that concept will probably not save you if your sync sucks. But it's possible. There are three things you can do with Concept. And this rule cheats, because you really need two things off it.
Have a theme. Your AMV should have a theme if possible. Something that ties the clips together in some way. Random scenes are not good. (Yes, a concept ties the clips together. That's what this rule IS.)
Tell a story. Alternately, instead of having a theme, you can tell a story with the clips. Maybe you think that Yui from Fushigi Yuugi is mistreated horribly. (Ballad of Yui Hongo) Well, you can tell that story with your AMV. Sure, this is a bit like having a theme, but it's different because it's a progressive theme instead of just something tying it together.
Do these things in a unique way. This is the rule that cheats. While it is possible for you to do one of these in a way that's just like everyone else's, it obviously will not be conducive to people remembering your video. I actually have a Dragon Ball Z/Linkin Park video that I kept out of that massive pile, because it was a very unique one. (Out of the pile of trash, there was one diamond.

Finally...
Third Rule: Opinion.
Opinion is sort of hard to shoot for. It's a direct RESULT of the first two, rather than something YOU do when you make the video. However, it is just as essential, and you should think about what opinions you may be evoking in your viewers. (And no, "This video rocks!!" does not count. But it is nice, isn't it?)
Makes you want to watch the anime. This is one of the marks of a good video. If watching your video causes someone to say, "Wow, I really need to see that anime!" then you did a good job on it. So, to shoot for this one, try to present the best clips possible from the anime you're using. Note that this doesn't work if you're doing a Various video with more than about two or three anime.
Makes you like the song. Assuming you didn't already like it of course - Enigma is a good example of this. (The video, that is.) If I had heard Frozen first outside that video, I probably wouldn't have liked it that much. But since the video was tied so well to it, I ended up liking the music more. To achieve this effect, you should try to tie your clips as closely as possible to the music, and your effects should also fit the music.
Just plain "fits". This is kind of a catch-all for the videos that fall through the other two. After all, maybe you've already seen the anime, and like the song! In this case, evoking the feeling that the music was made to fit the anime is the goal here. If you've succeeded in applying the tips in the last two rules, then this opinion will naturally follow.
An AMV usually has to take at least one of the rules from each of these. For Sync, usually two - but it's not necessary all the time (after all, what about a song without lyrics? How can you word- or lipsync to that?) I say that Rule Two cheats, but it really doesn't - you can make a unique video that doesn't have much of a theme. However, if you're choosing one of the other two, you'll probably want to make it unique, just to stand out. As for Opinion, it's hard to gauge except by having people watch.
Which brings me to my next (and final) point!
If you are just starting out, SHOW YOUR VIDEO TO OTHER PEOPLE BEFORE YOU RELEASE IT. Look over it yourself first of course, but get suggestions! Comments and criticism are NEVER BAD! Do you know why people cringe when they see "This is my first video..."? It's because too many people DO NOT DO THIS. They simply release what they have without touching it up, fine-tuning, etc.
Once your timeline is full, you are NOT DONE. Go back and look it over, preferably with someone. Make sure you are happy with every scene! If you find yourself saying, at any time, "Well, this scene isn't that great, but..." stop right there and find a better scene. It exists, or you wouldn't be saying that. If it truly was the best or only scene that could fit there, you would not say that to yourself. That uneasy feeling is your subconscious telling you "I've seen something that would fit better here!" Filler is not okay.

I hope this helps someone.
